The present invention relates to a learning proximity detector, for example of the inductive type, delivering a binary output signal for the presence or absence of a target and having a learning mode in order to achieve self-adaptation of the detector""s range relatively to a target and relatively to an environment.
The detection distance specific to such a device varies from one detector to another and, for a same detector, varies according to the mounting and environmental conditions, in particular for an inductive detector embedded in a metal mass. Furthermore, certain applications require that the sensitivity of the detector may be changed depending on its use. It is therefore useful to be able to adjust the range of a proximity detector on its location of use.
Detectors having a learning mode during which the detector is adjusted, in addition to a working mode corresponding to the normal operating mode of the detector, are already known (see document EP 0740716). In DE 4331555, it has also been suggested that a proximity detector be adjusted by using a processing unit to which is connected a non-volatile memory which, in a learning phase triggered by a sampling signal, stores a switching threshold determined from the comparison between the value of an internal counter and the value of the detection signal from the sensor. Moreover, in document DE 4006893, the adjustment component of the proximity detector consists of a nonvolatile memory which drives several resistive elements by means of a digital word, wherein the direction of variation of this memory may only be determined through the action of an operator.
The object of the invention is to design a proximity detector capable of adjusting the detection range not only according to a type of target to be detected but also according to the general environment of the detector, so that it may automatically and rapidly adapt to different multiple uses. Too large electrical power consumption from the detector in the working mode should also be prevented as desired, notably so that the acceptable leak current is not exceeded, especially for proximity detectors with an output of the two-wire type. This implies that the detector should be capable of operating in the working mode without excessive consumption related to the processing unit and without storing the switching threshold from the learning mode in a memory connected to the processing unit. Also, during the learning mode, the possibility of the operator sending instructions to the detector and also receiving feedback information indicating the current state of the detector, is of interest, altogether while retaining a simple and economical solution. Finally, it is desired that solutions be used which provides for far-reaching miniaturization of the detector.
For this, the invention describes a proximity detector comprising a sensor unit capable of delivering an analog signal according to the distance of a target, a detection stage capable of delivering a detection signal resulting from the comparison between the analog signal and a switching threshold, an output stage for amplifying and shaping the detection signal in order to deliver the detector""s output signal, and a processing unit receiving the detection signal as an input. The detector is designed for operation according to a learning mode corresponding to the adjustment of the detector""s range and according to a working mode corresponding to the normal operating mode of the detector. It is characterized by the fact that the detector comprises a variable digital storage resistor, driven by the processing unit and connected to the detection stage so that variation of the value of this variable digital storage resistor causes a variation of the switching threshold. During the learning mode, the processing unit acts, depending on the state of the detection signal, on the value of the variable digital storage resistor in order to determine a set operating value for the variable digital storage resistor, wherein this set operating value is applied during the working mode. During the working mode, the processing unit is in a standby state.
Moreover, the detector comprises conversing means connected to the processing unit, notably so that the learning mode or the working mode may be selected by an operator and also that the operator may be informed on the state of the detector.
The learning mode for the detector either comprises a short learning mode wherein teaching of the detector is only performed relatively to its environment, or a long learning mode wherein teaching of the detector is performed relatively to its environment and relatively to a target placed at a distance from the detector.